This invention relates to a fuel injection control method for supplying fuel through injection to a plurality of cylinders of an internal combustion engine, and more particularly to a method of this kind, which is adapted to perform a fail safe function in the event of occurrence of an abnormality in cylinder-discriminating means which determines the sequence of injection of fuel into the cylinders of the engine.
Among fuel supply control methods for electronically controlling the valve opening period of a fuel metering device of an internal combustion engine, for control of the quantity of fuel being supplied to the engine, a method has been proposed, e.g. by the assignee of the present application in Japanese Provisional Patent Publication (Kokai) No. 57-137633, which is adapted to first determine a basic value of the above valve opening period, i.e. the fuel supply quantity, as a function of engine rpm and intake pipe absolute pressure and then correcting the basic value thus determined by adding to and/or multiplying same by constants and/or coefficients being functions of parameters indicative of operating conditions of the engine such as engine coolant temperature, throttle valve opening, exhaust gas ingredient concentration (oxygen concentration), etc., while at the same time determining the timing of fuel injection into individual ones of the engine cylinders, from pulses of a top-dead-center signal generated at predetermined crank angle positions of pistons within the individual engine cylinders, as well as from pulses of a cylinder-discriminating signal indicative of a predetermined crank angle position of a piston within a particular engine cylinder, and driving fuel injection valves of the fuel metering device in accordance with the corrected fuel supply quantity and the determined fuel injection timing.
In such fuel injection control method, it is essential that pulses of the cylinder-discriminating signal which controls the timing of fuel injection into the engine cylinders as well as pulses of the top-dead-center signal should be generated accurately in predetermined sequence, to ensure smooth operation of the engine. The top-dead-center signal is generated by top-dead-center detecting means, pulses of which are each indicative of a predetermined position of a piston within a corresponding engine cylinder with respect to the top dead center of the same cylinder, while the cylinder-discriminating signal is generated by cylinder-discriminating means, pulses of which are each generated each time the crankshaft of the engine rotates through a predetermined angle with respect to a predetermined position of a piston within a particular engine cylinder. While the top-dead-center detecting means and the cylinder-discriminating means are both normally operating, a first one of a plurality of engine cylinders, e.g. four engine cylinders in the case of a four-cylinder engine, is supplied with injected fuel upon generation of a pulse of the top-dead-center signal generated immediately after generation of each pulse of the cylinder-discriminating signal, and the third, fourth and second cylinders of the four-cylinder engine are successively supplied with injected fuel in the mentioned sequence, in synchronism with the succeeding pulses of the top-dead-center signal. Thereafter, in the same manner as above, as further pulses of the cylinder-discriminating signal are generated, the engine cylinders are successively supplied with injected fuel in the above predetermined sequence in synchronism with successive pulses of the top-dead-center signal generated immediately after the respective preceding pulses of the cylinder-discriminating signal.
However, in the event that an abnormality occurs in the cylinder-discriminating means, such as disconnection of the wiring system, it is very likely that there is no generation of any pulse of the cylinder-discriminating signal or a pulse of the same signal is not generated through each predetermined angle of rotation of the crankshaft of the engine, that is, pulses of the same signal are generated at irregular intervals. In such event, it is impossible to attain the proper sequence of successive fuel injections into the engine cylinders in synchronism with pulses of the top-dead-center signal, which depends upon generation of pulses of the cylinder-discriminating signal. This results in the difficulty or impossibility of continuing smooth operation of the engine or degradation of the driveability of the engine, and can even result in stall of the engine.